The present embodiments relate to a power converter system.
In the case of medical investigation equipment such as, for example, a system for X-ray diagnosis or a magnetic resonance (MR) system, high voltages may be required for the generation of X-ray beams or electromagnetic fields. For example, in the case of X-ray equipment for baggage, freight or material checking, or in the case of tests on materials, high voltages are required. The power of the high voltage required lies in the range from a few kW up to over 100 kW, for example. In the case of computer tomography (CT) approximately 120-150 kW are required, for example. For angiography X-ray equipment (AX), approximately 80-100 kW may be required. For mammography investigation equipment, approximately 5 kW may be required, and in the case of an X-ray scanner for baggage checking, approximately 40-60 kW may be required.
FIG. 1 shows a block diagram of the generation of a high voltage (e.g., for a computer tomograph). In a first stage 10, an intermediate voltage 20 is produced from a mains power supply 17 (e.g., a 400V three-phase supply). The first stage 10 incorporates a mains rectifier 14, an intermediate circuit filter 15, an inverter 16, and an intermediate voltage transformer 12. From the alternating current input 17, a DC voltage 18 is produced using the mains rectifier 14. The DC voltage 18 is smoothed by the intermediate circuit filter 15 so that a smoothed voltage 19 is available for the inverter 16. The inverter 16 produces an alternating voltage with a significantly higher frequency than the frequency of the input voltage 17, and feeds the produced alternating voltage to the intermediate voltage transformer 12. In the intermediate voltage transformer 12, the alternating voltage is transformed, for example, to approximately 2000V. This intermediate voltage 20 is fed into a second stage 11. The second stage 11 includes a high-voltage transformer 13, a high-voltage rectifier 21, and a high-voltage capacitor 22. The high-voltage transformer 13 transforms the intermediate voltage 20 to a desired high voltage 23 of some thousands of volts. From this, the high-voltage rectifier 21 produces a DC voltage 24, from which a smoothed high voltage 25 is produced (e.g., for an X-ray tube 26) with the help of the high-voltage capacitor 22. This type of high voltage production requires high-cost semiconductor switches with high voltage strength and large and expensive transformers. The semiconductor switches may be realized, for example, by bipolar transistors with insulated gate electrodes (e.g., IGBTs).
In magnetic resonance systems, use is also made, for example, of cascade inverters (e.g., as is disclosed in DE 102006060417 B4). In the cascade inverter, the required current handling capacity is achieved by connecting IGBTs in parallel. However, a comparatively larger and more expensive transformer is provided with n-fold secondary windings in order to produce the galvanically separated supply voltages for the cascade cells.
From the field of oncology treatment systems, a circuit arrangement as shown in FIG. 2 is known. The circuit arrangement includes a power modulator and a transformer 206. The power modulator shown in FIG. 2, which includes two Marx generators 201 and 202, drives two primary transformer windings 203 and 204 in a common mode form of operation. From a supply voltage from a supply source 205, the Marx generators 201 and 202 produce an intermediate voltage that, with the help of the transformer 206, is transformed to a high voltage. Because the primary windings 203 and 204 of the transformer 206 are driven in a common mode form of operation, a demagnetization is provided. The Marx generator serves to produce transient voltage pulses of very short time duration and high amplitude. The Marx generator is based on the idea of using a DC voltage to charge up a large number of capacitors in parallel to the value of a stage voltage and to connect the capacitors in series. While the capacitors are connected in parallel and charging up, the charge currents add to each other. During the subsequent series connection, the voltages across the capacitors add to each other.